In the last year I have run campaigns using Pathfinder, Dungeon Crawl Classics RPG, The Burning Wheel, Mouse Guard, and Traveller. The internet tells me that this variety of games is somewhat atypical. If my gaming groups are an analog for any other, the system groups use is largely decided by the GM. It makes sense. Game Masters tend to be the most experienced members of a group and usually have the best familiarity with the ruleset. The internet also tells me that most groups have a dedicated GM. This means that the group is often playing that person's favorite game. This is how it should be. Between learning the rules and all of the out-of-game prep, GMs typically have the largest investment in a campaign.
Speaking from experience, I have yet to play a system that does everything well. As much as I love DCC RPG, I think it fails to do anything to encourage deep, character driven storylines. The reason I don't fault it for such is because it is clearly not trying to be that game. What it does well—pulp fantasy, dungeon crawl, "Appendix N" adventures"—it does better than any other system. But I don't always want that, and many groups don't always want what the GM has to offer.
The question is: how do you get a group to try a new system? The Golden Rule: play anything, but only GM what you want. There are far too many great, innovative games to get stuck playing the same one forever, but convincing a GM to look into a new system isn't easy. Offering to don the mantle of GM for some time is likely to be welcomed, as it is an incredible amount of work. It's overwhelmingly been my experience that groups benefit from having multiple people capable of running games as well as playing as many games as possible.